For a non-volatile memory, such as a NAND flash memory, the specific operational features of which are that the smallest unit for “erase” is “block” and the unit for “read” and “write” is “page”. When the information in a “page” is accessed, the information of the whole “page” is stored in an external memory, and when the RAM is not big enough, the internal sense amplifier is used to store the information of the whole “page”, and any data in that “page” can be accessed when the random data input/output is used. Thus, the importance of a buffer, especially the sense amplifier towards a non-volatile memory goes without saying.
In the structure of a NAND flash, the “0” and “1” of the size of a sensing current is defined according to the operating timing. Thus, the various clock timing is required under different conditions. If a stable clock is used, it will result in the sensing noise and the window loss.
It is worth to think about how to tune the clock timing easily in the related areas of the non-volatile memories. If a stable clock is given, that will cause boundary shift of “0” and “1”. If the trend of the temperature coefficients of a stable clock and that of the circuit are in the opposite directions, then it will cause even higher window losses. FIG. 1 shows a read sequence for a voltage sensing flash memory, and that is: Pre-charge, Developing, Charge sharing, and Strobe. Among these, Pre-charge means to pre-charge the bit line (BL) to setup the drain side level, Developing means to discharge the BL to setup the drain side level, Charge sharing means the voltage levels of the bit line and that of the node SEN charge share (or maybe the node DSEN as shown in FIG. 5(a)), and strobe means to strobe the sensing data. Thus, how to create a tracking sensing circuit to monitor the sensing operations of, e.g., Pre-charge time, Developing time, Charge sharing time and Strobe time is highly demanded.
Keeping the drawbacks of the prior arts in mind, and employing experiments and research full-heartily and persistently, the applicant finally conceived a flash memory with a read tracking clock and a method thereof.